Hot rolling method for obtaining wire rod

ABSTRACT

A hot rolling method for obtaining wire rod or the like of small cross section and with a high quality surface, particularly for copper wire rod, comprising the steps of rolling the initial product in a multi-stand rolling mill including assemblies each with a number of rolls, simultaneously pickling the product being rolled, and raising the specific pressures generated during the hot rolling to the very high values which derive from working on wire rods below 6 mm. diameter and down to 2 mm. diameter.

lJnited States Patent 11 1 Properzi HO'f IIDLLING METTIUTfiTIT OBTAINING WIRE ROD [76] Inventor: Ilario Properzi, Via Vittor Pisani 8,

Milan, Italy 1 [22] Filed: Oct; 28, 1971 [2]] Appl. No.: 193,435

[30] Foreign Application Piioritybata T Feb.20, 1971 Italy ..208l2/71 1 521 us. (:1 72/39, 72/201 [51] Int. Cl B2lb 45/04, B2lb 45/02 [58] Field of Search 72/39, 41-45,

[56] 1 References Cited UNITED STATES PATENTS 1,835,462 12/1931 Busey 72/39 3,529,998 9/1970 Singer 134/2 Primary Examiner-Charles W. Lanham Assistant Examiner-E. M. Combs Attorney, Agent, or Firm-Dr. Guido Modiano; Dr. A1- bert Josif 5 7 ABSTRACT A hot rolling method for obtaining wire rod or the like of small cross section and with a high quality surface, particularly for copper wire rod, comprising the steps -0f rolling the initial product in a multi-stand rolling mill including assemblies each with a number of rolls, simultaneously pickling the product being rolled, and raising the specific pressures generated'during the hot rolling to the very high values which .derive from working on wire rods below 6 mm. diameter and down to 2 mm. diameter.

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WERE ROD BACKGROUND OF THE INVENTION The present invention relates to a hot rolling method for obtaining wire rod or the like of small cross section and with a high quality surface. The method is particularly suitable for producing copper wire rod.

Copper wire rod, for example for electrical uses, is conventionally obtained by hot rolling wire bars, semicontainuous cast billets or a continuous ingot obtained by various continuous casting methods.

Rolling is normally continued until wire rod is obtained with a diameter of about 6 mm. After rolling pickling takes place, and consists normally of immersing the coils of wire in tanks containing firstly a pickling liquid, then a wash liquid and possibly a protective liquid. In the case of continuously produced wire rod, these operations can be carried out at the exit of the rolling millinside pipes in which liquids or gases flow which pickle and wash the wire rod before it is coiled.

The wire rod thus obtained has a powdery and irregular surface, which does not allow easy and economical drawing without breakages or scaling etc.

Moreover the need has arisen for producing wire rods having a diameter less than 6 mm. However in wire rod as thin as this, certain defects which in a certain manner are inherent in wire rods having a diameter of 6 mm. upwards, such as defects arising from the existence of cracks in the structure and surface of the wire rod, appeared to prejudice those drawing qualities which in practice are necessary for these wire rods. In fact in continuing to apply pressure for reducing the diameter of the wire rods by means of conventional rolling powdery and irregular surfaces, and when drawing in order to obtain wires having diameters less than 6 mm. it is consequently often necessary, particularly if thin or very thin wires are to be obtained, to carry out previous scalping or so called surface shaving operations on the hot rolled wire in order to eliminate the residual oxides and other defects of compactness and homogeneity. These operations require complex and slow machines and inevitably give rise to metal losses. In other words these operations are very costly.

Attempts have been made to obtain wire rod having a diameter less than 6 mm. directly by rolling, but the practical results have been unsatisfactory both because of the difficulties encountered in rolling and because of the considerable amount of material losses. In fact, on diminishing the diameter of the wire produced, the surface exposed to the air increases weight for weight because of which surface oxidation becomes considerable. Consequently the pickling which has to be carried out on the rolled product causes considerable loss of material which has a negative effect on production costs.

SUMMARY OF THE INVENTION An object of the present invention is to obviate the aforementioned disadvantages relative to methods presently in use for the production of wire rod of small diameter, by providing a method by means of which it is possible to obtain wire rods having a diameter less than 6 mm. which are not affected by defects deriving from cracks inherent in said wire rods, i.e. defects which could still be found when the wire rods, during previous stages of the process being carried out, had already reached a diameter which was low but still greater than 6 mm.

Another object of the invention is that of providing a method which can be easily carried out by utilising rolling equipment of conventional type, without the need for using machines for surface shaving or other auxiliary equipment.

Another object of the invention is to make available a method which is particularly suitable for use in con-- BRIEF DESCRIPTION OF THE DRAWINGS Further characteristics and advantages of the invention will be more evident from the detailed description of a preferred but not exclusive embodiment of the process according to the invention illustrated by way of example with reference to the accompanying drawing in which:

FIG. 1 is a frontal diagrammatical'view of a rolling mill for wire rod, according to a preceding patent of the same applicant, usable in the process according to the invention;

FIG. 2" is a cross section through an assembly of the rolling mill of the preceding figure;

FIG. 3 is aview of a rolling mill of old type (accord ing to another previous patent of the same applicant);

FIG. 4 is a cross section through an assembly of a rolling mill of old type (according to another previous patent of the same applicant).

DESCRIPTION OF THE PREFERRED EMBODIMENT In order to better clarify the present invention, the successive inventivestages followed by the applicant in his preceding studies will firstly bementioned.

Starting froma certain type of rolling mill, such as that described in the Italian Patent No. 449661 in the name of the same applicant (FIG. 3 refers to this patent), an improved rolling mill was developed such as that described in the Italian Patent No. 486369, again of the same applicant '(see FIG. 4). The development was thus from rolling substantially in the air to rolling by way of compact assemblies in which a cooling and lubricating system using a single liquid was provided for the rolls, the wire rod and the driving gears.

A further improvement was described in the Italian Patent No. 796085 or the corresponding U.S. Pat. No.

3552164 of the same applicant (FIG. 2 refers to this patent, in which one path for the lubricating liquid was predisposed for the gears and another path (which was distinct from the first) for the liquid used for cooling and/or lubricating the rolls and wire rod.

Finally the U.S. Pat. application Ser. No. 56.992 filed on May 25, 1970 by the same applicant now U.S. Pat. No. 366891 I, described a channel connection between one rolling assembly and the other so as to make the wire rod being rolled travel constantly immersed in the cooling and/or lubricating liquid of the rolls (FIG. I refers to this latter patent).

It can be thus seen that development has taken the path of a continually greater protection of the metal during rolling so that it should not become further oxidised during rolling. These arrangements led to the production of wire rods, particularly copper, of a greater quality than those offered on the market up to that time.

The invention takes development one step further.

In effect the process according to the invention is carried out by using a rolling mill constructed preferably according to the aforementioned Italian Patent No. 796085 or corresponding U.S. Pat. No. 3552164 (FIG. 2) and U.S. Patent application Ser. No. 56.992, filed on May 25, 1970 (FIG. 1), now U.S. Pat. No. 3668911.

More precisely each assembly. (FIGS. 1 and 2) of the rolling mill comprises separate paths for the lubricating liquid for the gears (as shown by the broken arrows 7 in FIG. 2), and for the cooling and/or lubricating liquid for the rolls 1 and wire rod 2 (continuous arrows).

This latter liquid is retained by tank member 6 (FIG. 1) disposed between one assembly and another.

The rolls 1 are disposed at 120 one to the other (FIG. 2) and the wire rod 2 being rolled is made to pass as stated immersed constantly. in the cooling and/or lu bricating liquid fed to the assemblies from above, at 3, and discharged lowerly, at 4. The path of this liquid is represented by the continuous arrows in FIG. 2.

According tothe present invention, a special solution having a pickling action (for example a mixture of water and methyl alcohol) is added to said cooling and- /or lubricating liquid.

Thus a cooling and/or lubricating and, at the same time, pickling liquid is obtained which is fed at 3 to each assembly of the rolling mill, and makes contact with the rolls 1 and wire rod 2, then discharging lowerly at 4 and over-flowing between one assembly and another at said tank members 6 (FIG. 1) disposed about the rolling axis so as to form a type of channel for said liquid these tank members are described in the aforementioned U.S. Patent application Ser. No. 56.992 filed on May 25, 1970, now U.S. Pat. No. 3668911.

FIG. 2 shows an assembly with an upper input shaft, but obviously the disposition is the same for assemblies with a lower input shaft (for further details see the aforementioned Italian Pat. No. 796085, or corresponding U.S. Pat. No. 3552164.

The arrangement provided in the prior designs by the same applicant, for assuring the immersion in liquid of the wire rod being rolled, led to a reduction in its surface oxidation, but a successive light pickling operation was still required, whereas the fissures between one crystal and another, the more visible rolling cracks not eliminated by successive compression, or other defects pre-existing in the initial ingot could not guarantee the surface homogeneity needed for good successive drawing, without breakages, scaling or other defects.

It is known that the power necessary for rolling a bar through a rolling mill increases rapidly as the diameter of the rolled product diminishes. For example in a tandem rolling mill with close assemblies and with approximately constant reductions in area of about 18 percent between one assembly and another, if the power absorbed by the first assembly is 6 HP, then the power absorbed by the 17th assembly is about 60 HP (for example in the production of 6 mm. diameter wire rod starting from a hot copper bar of 38 mm. diameter).

The invention deliberately exploits the fact that while the load exerted by each roll on the metal increases, the contact surface through which the force is transmitted from the cylinder to the metal diminishes as the diameter of the rolled bar diminishes. This means that the specific pressure on the surface of the metal rises to very high values.

It has been found that a critical value exists beyond which these specific pressures, in particular circumstances which will be-described, produce self welding between those points of the wire rod divided by said cracks or superficial irregularities. It has in fact been found that the critical threshold corresponds to specific pressures which are generated when rolling wire rods less than 6mm. diameter and down to 2 mm. diameter.

More particularly it has been found that the efficiency of the self welding action on the superficial irregularities is proportional to the absorbed powers, which in the example previously given are in the ratio of6 to 60, Le. ten times greater for the outlet assembly than for the inlet assembly. This is due to the considerable increase in specific pressures which arise when passing from the inlet assembly to the outlet assembly.

The particular circumstances previously mentioned arise when pickling action is simultaneously combined with rolling action, with hot rolling and pickling being carried out through a plurality of rolling assemblies of the type comprising three rolls at This action becomes continually'more efficient as diameters become smaller, so giving better quality surfaces.

The addition of pickling solutions according to the process of the invention means that the most minute interstices or cracks contained on thesurface of the bar are reached by pickling action. Moreover the continuous compression action of the rolls through the rolling mill exerts a pressure welding action between the purified metallic particles in the surface of the bar.

In practice it has been found that the action of the rolls is more efficient the greater the specific pressures exerted on the wire rod by the rolls. In particular the very high specific pressures necessary for reducing the diameter of rolled wire rod below 6 mm. are very effective, as stated.

By utilising the method according to the invention for producing wire rod with diameters less than 6 mm. (for example wire rod of 3 mm. diameter) results are obtained such as to make this type of wire rod preferable to that obtainable by conventional techniques.

Any further drawing of this special copper wire rod is easy and reliable, and the wire is produced with economical and technical advantage because the operation is almost exempt from breakage and moreover, as it is possible to start from a smaller diameter, the drawing operation is made easier. In substance, in the case of rolling to diameters less than 6 mm, the process according to the invention allows the application of an ultracompression under hot conditions of the surface being pickled, so that the surface integrity of the rod being formed is automatically reconstituted. This takes place independently of any defects existing upstream of the rolling mill. This reconstitutable surface integrity, unknown in the art until the present time, also gives rise to a greater tolerance of impurities contained in the metals (in particular in copper) and makes it possible to use materials of poor quality even for the production of thin wire.

Of course the method according to the invention can be used in plant for the production of wire rod of any type, both already existing and newly designed.

The application of the method according to the invention is very advantageous in plant for the continuous production of wire rod using continuous casting methods, for example with casting wheels according to previous designs of the present applicant.

The plant may comprise, for example, a wheel casting machine followed by a rolling mill in which the method according to the present invention is utilised, it in its turn being followed by a winding machine for the wire rod.

The invention thus conceived is susceptible to numerous modifications and changes may be made therein without departing from the scope of the invention as defined by the following claims.

In practice the pickling substances used may be modified according to requirements and any method of feeding said substances may be used.

I claim:

'1. A hot rolling method for obtaining wire rod or the like of small cross section and with a high quality surface, particularly for copper wire rod, by rolling the wire rod in a multistand rolling mill having a plurality of rolling assemblies, wherein the wire rod is contacted with a liquid solution having a pickling action for maintaining the surface of the wire rod free of oxide during rolling, and wherein further simultaneously to pickling said wire rod is subjected to a rolling action reducing its cross section to a diameter less than 6 mm. thereby increasing the specific pressure on the surface of the wire rod being rolled and simultaneously pickled to have a reconstitution of the surface integrity of the wire rod by a self-welding of the cracks and the like existing on said surface. 

1. A hot rolling method for obtaining wire rod or the like of small cross section and with a high quality surface, particularly for copper wire rod, by rolling the wire rod in a multistand rolling mill having a plurality of rolling assemblies, wherein the wire rod is contacted with a liquid solution having a pickling action for maintaining the surface of the wire rod free of oxide during rolling, and wherein further simultaneously to pickling said wire rod is subjected to a rolling action reducing its cross section to a diameter less than 6 mm. thereby increasing the specific pressure on the surface of the wire rod being rolled and simultaneously pickled to have a reconstitution of the surface integrity of the wire rod by a self-welding of the cracks and the like existing on said surface. 